Method of and apparatus for annealing



Nov. 13, 1962 L. WILSON METHOD OF AND APPARATUS FOR ANNEALING 4Sheets-Sheet 1 Filed May 7, 1958 INVENTOR. [5 M4 :0

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METHOD OF AND APPARATUS FOR ANNEALING Filed May 7, 1958 4 Sheets-Sheet 2INVENTOR. LEE M4 sa/v BY M M,

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L. WILSON METHOD OF AND APPARATUS FOR ANNEALING Nov. 13, 1962 4Sheets-Sheet 3 Filed May 7, 1958 INV ENT OR. (5 ML 50 Nov. 13, 1962WILSON METHOD OF AND APPARATUS FOR ANNEALING 4 Sheets-Sheet 4 Filed May7, 1958 J WW m MW 1m M A .H/ 6 HM .K K M United States Patent 3 063 878METHOD OF AND APFAR ATUS FOR ANNEALWG Lee Wilson, Rocky River, Ohio. LeeWilson Engigelfiriiig Co. Inc., 20005 W. Lake Road, Cleveland 16,

Filed May 7, 1958, Ser. No. 733,762 14 Claims. (Cl. 148-433) Thisinvention relates to the annealing of metals and more particularly to animproved method of and apparatus for annealing coils of metal strip.Specifically, my invention involves certain novel procedures andapparatus whereby the time required for and cost of annealing coils ofstrip metal is greatly reduced from prior commerical practices.

In the copending Lee Wilson and Edwin A. Corns United States patentapplication Serial No. 639,939, filed February 13, 1957, there isdisclosed a method of and apparatus for annealing coils of strip metal,with particular reference to cold roll steel strip, wherein a tightwound coil of strip metal is opened into a coil having its laps orconvolutions spaced apart from each other by a distance from aboutone-half to about three times the thickness of the strip. The thusopened coil is maintained with its axis vertical and heated by forcing aheated gaseous atmosphere at high velocity through the spaces betweenthe laps of the opened coil. As is fully explained in said copendingpatent application, the opened coil annealing of strip steel byconvection heating from high velocity gaseous atmosphere enables a coilto be brought up to annealing temperature in a small fraction of thetime required by previous annealing systems in which the tightly woundcoil was heated by the application of heat to the external ends and sidewalls thereof. Depending on the dimensions of the coil being handled,the surface area of an opened coil available for direct heat transfer tothe strip is from about two hundred to about one thousand times thesurface area available for heat transfer with a tight coil.

As is also pointed out in said copending patent application, the heatingof an opened coil for annealing purposes may be etfected in a bell typefurnace. A single opened coil is shown as being heated within an innercover in a bell type furnace in the said Wilson and Corns patentapplication, and apparatus for annealing a plurality of opened coilsstacked one upon another is described and claimed in the copendingpatent application of Calvin C. Blackman and Robert J. Beemer Serial No.703,905, filed December 19, 1957 and owned by the applicant herein.

Although the annealing of opened coils in a bell type furnace is a greatimprovement over the annealing of tight wound coils in such furnaces,the full possibilities of opened coil annealing are not achieved in hellfurnace installations.

Accordingly it is an object of the present invention to provide a methodof and apparatus for annealing opened coils of strip metal whereby greatsavings are effected in first cost of the apparatus required to producea given output, operating costs are greatly reduced as compared toprevious procedures, a better and more uniform product is obtained,control of the annealing operation is facilitated, the time required forannealing a coil of a given size and weight is greatly reduced, and theinventory of coils in process is much less than that required wheretight wound coils are annealed in hell type furnaces.

Other objects of my invention include the provision of an improvedtraveling hearth recuperative type annealing furnace whereby asubstantial portion of the heat applied to the strip to anneal same isrecuperated or recovered and transferred to preheat other coils thathave not been 3,063,878 Patented Nov. 13, 1962 brought up to annealingtemperature; the provision of a traveling hearth annealing furnacewherein an atmosphere of inert gas may be mantained to preserve thefinish of the metal strip and prevent oxidation thereof duringannealing; and the provision of means for supporting the opened coilsfor loading into the furnace, treatment in the furnace, and Withdrawalfrom the furnace which facilitates the desired flow of'atmospherethrough the opened coils during annealing and greatly simplifies thecoil handling problem.

The above and other objects of my invention will appear from thefollowing description of my recuperative traveling hearth furnace and myimproved procedure for utilizing same. As illustrated in the drawingsattached hereto, and described more in detail later in thisspecification, my novel apparatus includes a furnace having a travelinghearth and a furnace chamber through which the opened coils to beannealed pass in step-by-step fashion. The traveling hearth carries aseries of spaced dividing walls which separate the furnace chamber intoa plurality of charge compartments. As the hearth is advanced insuccessive steps, the charge compartments progressively move to and areindexed at a series of charge treating stations where the variousheating and/or cooling steps are performed. Between each indexingmovement of the hearth each compartment remains at its particularstation for a predetermined period of time, and when the proper time haselapsed, the hearth advances one step to index each charge compartmentat the next treating station. At a certain station or stations heat isapplied to the coil from an external source by forcing heated atmospherevertically through the opened laps of the coils while at another stationor stations the coils that have been heated to annealing temperature andsoaked for the proper time are cooled by a circulating body of gaseousatmosphere which is forced through the hot coil and then throughsuitable ducts to another coil in a charge compartment disposed at apreheating station in advance of the heating station so that theincoming coils are preheated by heat derived from the cooling of thecoils which have been subjected to annealing temperatures. .Thus arecuperative system is provided which results in a substantial reductionin fuel costs, my novel structure being such that the preheating, finalheating and soaking, and cooling operations may be carried out in a unitrequiring a minimum of floor space and of low first cost as compared toother coil annealing apparatus of equal output capacity.

The furnace illustrated in the drawings and specifically describedherein is of the rotary hearth type in which the coils under treatmentmove in a circular path. It will be understood, however, that myinvention may be incorporated in straight-through or linear furnaces inwhich the coils travel in a straight line, in so-called U-type furnaces,or other arrangements wherein the path of travel of the coils is notcircular.

Referring now to the drawings:

FIGURE 1 is a plan view of a rotary type traveling hearth furnaceaccording to my invention;

FIGURE 2 is a horizontal cross-sectional view of the furnaceinstallation shown in FIGURE 1, taken substantially on line 2-2 ofFIGURE 3;

FIGURE 3 is a vertical cross-sectional view through the furnacestructure shown in FIGURE 1, taken substantially on line 33 of FIGURE 1;

FIGURE 4 is a fragmentary vertical cross-sectional I view, takensubstantially on line 44 of FIGURE 2 and illustrating the rotary hearthdrive means;

FIGURE 5 is an enlarged detached plan view of one of the coil supportunits used in annealing opened coils in the furnace shown in FIGURES1-4;

r 3 FIGURE 6 is a vertical cross-sectional view taken substantially online 66 of FIGURE FIGURE 7 is an end elevation of the coil support unitof FIGURE 5 looking at the large or outer end thereof;

and

FIGURE 8 is an enlarged fragmentary plan View of a part of an openedcoil illustrating the spacing between the laps. V

The rotary hearth furnace illustrated in the accompanying drawings andwhich embodies the present invention includes an annular furnace chamberC defined by an outer wall 1, an inner wall 2, and a top wall or cover3. These walls are supported on a foundation or base 4 having an annularpit 5 projecting below the bottom of the annular furnace chamber C.

Supported on circular tracks 6, which rest on the base 4, is the rotaryhearth H. This hearth is annular in form and is supported on tracks 6 bya plurality of circumferentially spaced wheels 7. The inner and outeredges of the hearth H extend into close proximity to the inner and outerchamber walls 1 and 2, and suitable sealing means may be provided tomaintain the desired seal between the moving edges of the hearth and thestationary walls of the furnace chamber.

A circumferential rack 8 is mounted on the underside of hearth H and, asseen in FIGURE 4, is engaged by a drive pinion 9 carried on shaft 10.Shaft 10' may be driven by any suitable power means (not shown) such asan electrical motor, and, to effect rotation of the hearth H in thedesired step-by-step manner as will be more fully referred to later,timing and control means of any suitable and well-known type may beemployed.

A plurality of radially extending, circumferentially spaced, verticaldividing walls 11-17 inclusive are carried by and move with the rotaryhearth H. The edges of these walls are disposed in close proximity tothe outer, inner and top walls 1, 2 and 3 of the furnace chamber C and,in etfect, divide the furnace chamber C into a series of chargecompartments equal in number to the number of dividing walls. As thehearth H and the dividing walls 1117 have close fits within the annularfurnace chamber, each of the charge compartments formed by the dividingwalls may be maintained at difierent atmospheric or heating conditionsfrom that of the adjacent charge compartments. Furthermore, as thehearth H is rotated (as shown in the drawings in counter-clockwisedirection) in indexed step-by-step travel, the several chargecompartments will be moved successively between a series of chargetreating stations which are indicated on FIGURE 2 of the drawings by thereference characters I-VTI inclusive. It will be understood that whenthe hearth H is advanced a step, it will move a distance such that anygiven dividing wall will be moved into the previous position of the nextdividing wall ahead in the direction of rotation of the hearth. In otherwords, referring to FIGURE 2, when the hearth is advanced one step, thedividing wall 11 will move into the position of wall 12, Wall 12 willmove into the position of wall 13, etc. For reference purposes, theseveral charge compartments carried on the rotary hearth H will beidentified by the dividing walls at their ends. Thus, as seen in FIGURE2, the charge compartment disposed at station I is identified as chargecompartment 11-12, the charge compartment station disposed at station Vis identified as compartment 1516,.etc.

As best seen in FIGURE 2, a charge loading opening 18 is formed in theouter furnace chamber wall 1 at station I, and a charge discharge orunloading opening 19 is located at station VII. Suitable verticallymovable doors 20 and 21 respectively are adapted to close and open saidopenings 18 and 19. Outside of the main furnace chamber C at thecharging or loading opening 18 is an atmosphere lock and purge chamberP, and an atmosphere lock and cooling chamber F is similarly disposedoutside of the unloading opening 19. These chambers P and F have gastight connections with the exterior housing of the furnace and areprovided with outer vertically movable doors 22 and 23 respectively.

Tracks 24 support a charge loading carriage L for movement into and outof the purge chamber P and the furnace chamber C, and tracks 25similarly support unloading carriage L. Each charge compartment onhearth H also has a pair of tracks which align with and form extensionsof tracks 24 and 25 when the hearth is in its stationary indexedpositions. These hearth tracks are seen at 25 in FIGURE 2.

In order to advance and retract the carriages L and L, drive means areprovided adjacent each pair of tracks 24 and 25. Referring toFIGURES 2and 3, the drive means for unloading carriage L includes an inner pairof drive chains 26 and an outer pair of drive chains 27. These chainsare supported on suitable spaced sprockets and have their upper reachesextending generally at or slightly below the level of tracks 25. Theyare driven by the shaft 28 which in turn is connected through suitablegearing, etc. to a drive motor 29. Shaft 30 which drives the sprocketswhich support outer drive chains 27 is also driven by motor 29 through abelt or chain connection 31.

Interengaging dog or clutch means are provided on the underside of thecarriage L and on the drive chains 26 and 27 so that when these chainsare rotated in one direction the carriage will be advanced toward andinto the furnace chamber and, when they are moved in the oppositedirection, the carriage will be withdrawn. TWo sets of drive chains 26and 27 are provided so that the outer door 23 may be closed behind thecarriage when it is in the cooling lock or chamber F and the carriagethen advanced into the furnace chamber by action of the drive chains 26.The outer set of drive chains 27 will engage the pick-up devices on thecarriage L during outer movement thereof before the carriage is releasedfrom its driving connection to the chains 26, and thus drive chains 27will elfect movement of the carriage through the outer door 23 of thechamber F. Similar reference characters have been applied to thecorresponding drive chains, etc. which are disposed at the purge lock orchamber P for moving the carriage L, the two installations substantiallyalike in arrangement and function.

In order to provide the desired circulation of furnace atmosphere, aswill be fully explained later, the inner wall 2 of the furnace chamber Cis slotted just above the top surface of the hearth H at treatingstations VII and I. This slot is seen at 32 in FIGURES 2 and 3 andconnects the furnace chamber with an atmosphere conduit on passage 33which connects the lower portions of stations I and VII. Anotheratmosphere conducting pipe or conduit 34 extends from the top of stationI to the top of station VII, and a fan or blower 35 (see FIGURE 1) inconduit 34 is adapted to effect a circulation of atmosphere through theslot '32 from the bottom of station VII, through conduit 33, throughslot 32 to the lower part of station I, up through the coil in stationI, out through the top wall 3 of the furnace into conduit 34 and backinto the top of station VII. The atmosphere then passes downwardlythrough the coil at station VII, and this circulation is continued bytheblower 35 for purposes to be explained later.

In like manner a slot 36 through wall 2 at the lower part of station VIprovides a gas passage into the conduit 37 which extends across thefurnace and connects to another slot 38 at the lower part of station II.An atmosphere conducting pipe 39 extends over the top of the furnacefrom the top of station II to the top of station VI, and a fan or blower40 (FIGURE 1) is adapted to create and maintain a circulation ofatmoSphere through and between the charge compartments that are disposedat stations II and VI. In this instance the blower 40 is operated sothat the circulation is downwardly through the coil in the compartmentwhich is disposed at station II, across through lower conduit 37,v

upwardly through the coil in the compartment at station VI, and backacross over the top of the furnace through conduit 39 and into the topof the compartment at station II.

In order to supply heat to bring the opened coils being treated toannealing temperature, an outside heater unit A is disposed adjacentstation III of the furnace chamber. This heater unit includes a suitablesource of heat such as radiant combustion tubes 41, and a fan or blower42 is adapted to withdraw atmosphere upwardly from the chargecompartment at station III through a conduit 43, move this atmospherethrough conduit 44 into the heater unit A where it is heated by passingover the hot combustion tubes 41 (or other source of heat such aselectrical heating units or the like). After passing through the heaterA, the atmosphere travels through a bottom conduit 45 and a slot 46 inthe outer Wall 1 of the furnace into the charge compartment indexed atstat-ion III. The circulating atmosphere which is moved through thecharge compartment at station III transfers heat rapidly and mostefiiciently to the opened coil supported at this station.

A secondary atmosphere heater unit A is also disposed outside of themain furnace chamber adjacent stations IV and V. This unit is alsoheated by radiant tubes 47 or other suitable means. A gas conductingconduit 48 extends from the lower part of the heater unit A through aslot 49 in furnace wall 1 into station V just above the hearth H. Theupper part of station V is connected to the upper part of station IV byconduit means 50 (see FIGURE 1) in which is interposed a blower 51driven by a suitable motor 52. The lower part of station IV is connectedback to the heater unit through a slot 53 in outer wall 1 of the furnacechamber and conduit 54. In operation the blower 51 is driven in adirection which will effect circulation downwardly through the coil inthe charge compartment at station IV, through lower conduit 54 into theheater A, through the heater in contact with the radiant heating tubes47, out through lower conduit 48 and slot 49 into the lower part of thecharge compartment at station V, upwardly through the coil at station Vand out through the top thereof to blower 51 and back down through thecoil in station IV. The purpose of this application of heat, as willappear later, is to bring the coils up to final annealing temperatureand maintain them thereat for the desired soaking time.

In order to permit the opened coils to be charged into and removed fromthe furnace and properly to support the coils in the furnace so thatcirculation of atmosphere will be channeled directly through the coils,and substantial flow other than through the coils be prevented, Iprovide coil support units that are seen at S in FIG- URES 2 and 3 andare illustrated in detail in FIG- URES 5, 6 and 7. Each of the supportunits S includes a top bathe plate 61 having a circular central opening61' therein across which extends a perforate grid-like structure 62whereby an opened coil may be supported thereon with a minimuminterference with the flow of atmosphere through the opened laps of thecoil. The forward edge of the support unit S is arcuate as seen at 61"to conform to and be disposed in close proximity to the inner wall 2 offurnace chamber C when the unit is in one of the hearth charge chambers.The side walls 63 of the units S converge at their inner portions toconform to and closely fit the inner portions of the adjacent dividerWalls which define the several charge compartments on the hearth H. Inorder properly to support the upper face of the grids 62 in spacedrelation above the top of the hearth H, a plurality of bottom members 64are supported by a suitable reinforced trusslike structure 64'. Thesebottom members 64, however, are omitted in spaced parallel channels 64"so that the units S may fit over the carriages L and L' and be supportedon the hydraulic lifters 55 thereof so that they may be moved into andout of the furnace chamber.

When lifted by the lifters 55, the bottom members 64 of the supports Swill clear the top of the hearth H, and when a unit S is positioned inone of thecharge chambers on the hearth H, as seen in FIGURES 2 and 3,the lifters 55 may be lowered to permit the bottom members 64 to rest onthe top of the hearth H and to allow the carriages L or L to bewithdrawn. The open channels 64 also straddle or overlie the portions25' of the tracks 24 and 25 which extend into each of the chargechambers on the hearth.

The outer edge 61" of the bafiie plate 61 is curved to conform to thecurvature of the outer wall 1 of the furnace chamber C. Thus when asupport S is positioned in a charge chamber on the furnace hearth, theinner edge 61 of the top baflie plate is in close proximity to the innerwall 2 of the furnace chamber, and the outer edge is in close proximityto the outer wall -1 of the furnace chamber. The vertical side walls ofthe unit S are imperforate, and the coils that are disposed on the unitsS have outer diameters substantially equal to the diameter of thecircular opening 61 in the plate 61. Thus the units S not only act tosupport the coils above the furnace hearth but also positively toprevent any substantial flow of atmosphere through a charge chamberexcept through the opened laps of the'coil.

This is an important feature of my annealing system as, in order toobtain my improved heating eificiency, the flow ofatmosphere must becontrolled so that substantially all movement thereof is through thecoils, and little or no flow occurs around the outside ofthe coil ordown through the center thereof. 'Center flow is prevented by closingthe central portion of the coil supporting grid surface 62 or by puttinga plate over the top of the central opening in the coils before they arecharged into the furnace.

A plurality of slots or channels 62 extend radially of the top face ofthe units S to facilitate the insertion and removal of coil lifting barsbelow a coil supported on a unit S. Although it is preferred that allcoils being handled have an outside diameter substantially equal to thediameter of the circular opening 61' in the baffle plate 61, if a coilis smaller than this circular opening, bypassing of atmosphere may beprevented by wrapping a wire cable around on top of the grid or by othergap closure means.

In FIGURE 1 a coil support unit S is shown supported on the carriage L'on the hydraulic lifters 55 thereof. These lifters are adapted to raisethe unit S and the coil support thereon above the floor level so thatunit S and its coil may be moved along the tracks 25. In like manneranother unit S is shown supported on the carriage L outside of the purgechamber P and is adapted to be lifted and moved by the carriage L intothe purge chamber P.

Before a coil to be annealed is charged into the furnace chamber, it ismoved into the purge chamber P, the outer door 22 thereof being opened.While in the purge chamber P, and with both the inner and outer doors 20and 22 closed, a suitable gaseous atmosphere, for instance an inert orsomewhat de-oxidizing gas, is caused to enter the chamber P and passthrough the open laps of the coil and then to be exhaused from thechamber until all air has been purged from the chamber and the coil. Thecoil and chamber Pare now completely filled with the desired inert orother gaseous atmospher and, when the gate 20 is opened to permit thecoil to be charged into the furnace, there will be no escape or dilutionof the gaseous atmosphere in the furnace proper.

When a coil is completely annealed, it is disposed at the last stationVII. As it is supported on its coil support unit S, the carriage L maybe run under the units S when the door 21 is opened, the hydrauliclifters 55, or other suitable elevating means, operated to lift the unitS and coil from the furnace hearth, and the coil and support unit thenwithdrawn into the cooling lock chamber F. At

this time the outer door 23 is closed and chamber F is preferably filledwith the protective atmosphere so that the atmosphere in furnace chamberC will not be diluted by outside air while door 21 is open. The door 21is then closed, and the coil 1, which in the example given later, is inthe neighbor-hood of 450 F., may be subjected to forced cooling byoperation of a blower 56 mounted on top of the chamber F and adapted tocirculate the atmosphere in chamber F through a bottom conduit 57(FIGURE 3), the coil, and then down through an atmosphere cooling unit58 and back into chamber F. As seen in FIGURE 3, a hood 59 and flexiblesleeve or curtain 60 are adapted to fit over the'top of the coil beingcooled to channel the circulating cooling atmosphere through the openedlaps of the coil. When the desired cooling action has been completed,the door 23 may be opened and the carriage L moved out together with thecoil support S and'the annealed and cooled coil supported thereon. Thelock arrangement provided by the double doors 2i and 23 prevents theentry of outside air into the furnace chamber C while a coil is beingdischarged from station VII.

An example of the annealing of opened coils in the illustrated apparatuswill now be given, it being understood that the times and temperaturesmentioned may be varied to suit the size and type of coils beinghandled.

An enlarged fragmentary plan view of a portion of an opened coil isillustrated in FIGURE 8. It will be observed that each of the laps orconvolutions 75 are spaced apart by gaps or passages 76. As illustrated,these passages are approximately equal in width to the gauge of the:metal of the laps 75 but this spacing may be varied, preferably withina range-from about one-third to about .three times the strip gauge.

It may be assumed that the furnace hearth is in the position illustratedin FIGURE 2 and that one of the timed operating steps of the completecycle has just been completed. At this point in the cycle, the openedcoil in charge compartment 1711, which is now located at station VII, isready to be withdrawn from the furnace. Accordingly, the door 21 isopened, the carriage L is advanced until it is disposed below the coilsupport unit S on which the coil' at station VII is held, the hydrauliclifters 55 on carriage L' are raised to lift the coil support .nnit Sand coil'frorn the hearth H, carriage L is withdrawn into thecolingchamber F, the outer door 23 being closed, and the inner door 21is then closed.

The charge compartment 1711 is now empty and opened coils are disposedrespectively in charge compartments 1112, 12-43, 13-44, 1415, 15-16, and1617. Immediately after the annealed coil has been removed fromcompartment 1711, the hearth H is advanced or indexted one stepwhereupon the now empty compartment 1711 moves to station I, compartment1112 with coil 66 therein moves to station II, etc. As soon as thismovement of the hearth has been completed, the charging door 20 isopened and carriage L, together with a coil support S and a new coilthereon, is moved into the empty charge compartment. This coil, ofcourse, has ben purged of all air in purge chamber P as previouslyexplained and, when it is disposed in position at station I and carriageL withdrawn, the charging door 20 is closed.

An opened coil is now disposed in the charge compartment at each ofstations I-VII inclusive. The coil 66 at station I is substantially atroom temperature, and it will be subjected to recuperative heating bytransfer of heat from the coil 65 which has just been moved into stationVII. In a typical operation this 65 has been reduced to a temperature ofapproximately 900 F. By circulating furnace atmosphere downwardlythrough the 900 coil 65 at station VII, through conduit 33, up throughcoil 66 at station I, and then through blower 35, conduit 34 and againdown through coil 65, the temperatures of the two 'coils maybe'substantially equalized, i.e., the temperature of coil 66 at stationI may be brought up to about 450F.

and the coil 65 at station VII may be brought down to about 450 F.

In the typical operation being described the time of dwell of the hearthH at each treatment station is set at about one hour in order toproduce, for example, about twenty tons of uniformly annealed productper hour. However this time may be varied to suit the type and size ofcoils being annealed, or for other reasons.

While coil 66 at station I is being preheated, the coil 67 at station II(which has previously been given a first preheat at station I) is beinggiven an additional preheating by circulating furnace atmosphere upthrough coil 71 at station VI, across over the top of the furnacethrough the conduit 39, down through coil 67 at station II and backacross the furnace through lower conduit 37. Coil '71 enters station VIfrom station V at approximately annealing temperature, for example 1320F., and during the one hour treatment period its temperature will bereduced to approximately 900 F. while the temperature of the coil 67 atstation II will be raised from about 450 F. to approximately 900 F. Thusat stations I and II each coil is raised in temperature from roomtemperature to approximately 900 F. by heat recuperated from coils whichare being cooled to the temperature they are removed from the mainfurnace chamber.

During the same time period that the above preheating operations havebeen taking place, the coil 68 has been disposed in compartment 13-14 atstation III. This coil enters station III from station II atapproximately 900 F. and, by circulating heated gas from the heater A athigh velocity vertically through the opened coil 68, its temperature maybe raised during said time period approximately to annealingtemperature, for example about 1300 F.

As the coil at station III may be heated to a slightly highertemperature at the bottom than at the top because the hot gas fromheater A enters the coil at the bottom, the temperature is equalized atstation IV where the further coil is heated by atmosphere from anothergas heater A moving in the opposite direction downwardly through thecoil (69) at station IV. As the temperature of the coil is approximately1300 F. when it enters station IV, its temperature is equalized andbrought to the desired annealing temperature, for example 1320 F in afew minutes. The circulation of heated atmosphere at stations IV and Vis a series flow through the coils at these two stations, and the outputof the heater A and the rate of flow of atmosphere through blower 51 isso regulated that the coils are maintained at annealing temperature forpractically the entire two time periods during which they remain atthese stations. Thus each coil is soaked for a total of about two hoursat the proper temperature (1320 F. in this example) at the stations IVand V.

As previously explained, when a coil enters station VI, it is atannealing temperature, but while it remains at station VI, heat iswithdrawn and transferred to preheat the coil at station II so that acoil 71 at station VI is brought down from about 1320 F. to about 900 F.As also previously explained, the coil 65 at station VII arrived at thispoint from station VI at about 900 F. and, during its one hour timeperiod at station VII, it is reduced in temperature to about 450 F.while the new coil which has been charged into station I is pre heatedup to about 450 F.

' Upon completion of the seven one hour treating periods describedabove, the room temperature coil which entered station I has progressedthrough all seven stations and has been completely annealed and cooleddown to about 450 F. in a total elapsed time of between seven and eighthours, some time being required, of course, to effect the hearthmovements between the one hour periods and to unload a coil from stationVII, advance the empty compartment to station I, and loada new coiltherein between each one hour period.

It has been pointed out above that the flow of atmosphere through thecoil at station VII is downwardly and that through the coil at station Ithe circulation is upwardly. As has also beer pointed out, thecirculation at station II is downwardly, at station III upwardly, atstation IV downwardly, and at stations V and VI upwardly. Because ofthis reversal of flow of atmosphere through the coils at successivetreating stations, the heating and cooling action of the gas verticallyof the coils is substantially equalized. Thus at station I the heatedatmosphere passes upwardly through the coil and, as it is at its highesttemperature at the bottom of the coil, the temperature of the lower partof the coil at station I at the end of the treatment period at saidstation may be slightly greater than at the top of the coil. However,when the coil moves to station II, the flow of preheating atmosphere isdownwardly through the coil and the atmosphere from station V1 is at itshighest temperature at the top portion of the coil. Thus dilferences intemperature between the top and bottom of the coil are minimized. Inlike manner the reversal of flow at the succeeding stations equalizesthe temperature vertically of the coil during heating and soakingperiods.

Although I have illustrated and described a rotary hearth furnace havingseven charge treating stations, the number of stations may be varieddepending upon the type of treatment to be given to the charge. Thus, insome cases, only one pair of cooling and preheating stations may beemployed, or soaking may be effected in a single station rather than intwo as illustrated herein.

It will also be understood that in addition to a great reduction in thetime required for annealing a given quantity of material, the buildingspace required for an equivalent tonnage output is much less with myimproved apparatus and procedure than with previously used bell typecoil annealing furnace installations. Furthermore fuel costs aresubstantially reduced by my system because of the recuperative heatingof the incoming coils by the coils being cooled, a minimum of labor isrequired because the coils are handled a minimum number of times and forextremely short distances, the inner covers and coil spacers orconvectors commonly employed in tight coil annealing in bell typefurnaces are completely eliminated together with their relatively highcost and maintenance problems, and a better annealed product is obtainedbecause of the very uniform heating that can be accomplished throughoutthe coil. Sticking of the coils at the edges is completely eliminatedbecause the laps are spaced apart during the entire coil heating andcooling operation. Furthermore, because of the small number of coils inprocess at any given time, as compared to the number of coils in processto produce the same output by prior procedures, my system greatlyreduces the number of coils in inventory, thus increasing the workingcapital available for other purposes.

Although I have described the illustrated embodiments of my improvedannealing apparatus and have explained a particular procedure which maybe practiced therein, it will be understood that variations andmodifications may be made both in my apparatus and method withoutdeparting from the spirit of my invention. I do not, therefore, wish tobe limited to the exact embodiments herein illustrated and described butclaim as my invention all forms thereof coming within the scope of theappended claims.

I claim:

1. A rotary hearth annealing furnace for annealing opened coils of stripmetal having spaced apart laps including stationary walls defining agenerally annular continuous furnace chamber, a rotary hearth disposedat the lower part of said furnace chamber, a plurality of radiallyextending dividing walls carried by said rotary hearth and movabletherewith, said dividing walls extending in close proximity to saidfurnace walls whereby said furnace chamber is divided into a pluralityof charge compartments, means for supporting an opened coil of stripmetal in each of said charge compartments above said hearth and with itsaxis vertical, means for rotating said rotary hearth and chargecompartments in step-by-step movement and indexing said compartments ata series of charge treating stations in said furnace chamber, saidfurnace walls having charging and discharging openings at the first andlast of said stations respectively, door means for closing saidopenings, means for loading a charge into the charge compartmentdisposed at said first of said stations, means for withdrawing a chargefrom the charge compartment disposed at said last of said chargetreating stations, means for maintaining an artificial gaseousatmosphere within said furnace chamber, means for circulating between apair of charge compartments indexed at a particular pair of said worktreating stations the atmosphere contained therein whereby heat exchangeis etfetced between the charges in said pair of charge compartments, gasheating means disposed'outside of said furnace chamber, and means forrepeatedly circulating a body of said artificial gaseous atmospherevertically through another of said charge compartments disposed atanother of said charge treating stations and said gas heating meanswhereby the charge in said last named charge compartment is heated, eachof said means for supporting an opened coil of strip metal including abaflle plate disposed to direct substantially all of the atmospherebeing circulated through the charge compartments vertically through thespaced apart laps of opened coils disposed on said supporting means.

2. An annealing furnace for annealing opened coils of strip metal havingspaced apart laps including a traveling hearth having a plurality ofcharge support means spaced thereon and a plurality of dividing wallssupported thereby and defining the ends of a series of chargecompartments in each of which is one of said charge support means,stationary walls defining a continuous furnace chamber overlying saidhearth and having a series of charge treating stations, means fortraveling said hearth through said furnace chamber in step-by-stepintermittent movement whereby each of said charge compartments is movedto and from each of said'series of charge treating stations, said seriesof stations including a first charge loading station, a last chargedischarge station and intermediate stations therebetween, atmosphereheating means disposed outside of said furnace chamber, means forcirculating atmosphere in a closed path through said heater andvertically through the charge compartment at one of said intermediatestations whereby the charge in said charge compartment will be heated,and means for circulating atmosphere vertically through a pair of chargecompartments disposed respectively at stations preceding and following,in the direction of hearth travel, said one of said intermediatestations whereby heat from the charge in the compartment at saidfollowing station will be transferred to the charge in the compartmentat said preceding station, each of said charge support means including abaffle plate disposed to direct substantially all of the atmospherebeing circulated through the charge compartments vertically through thespaced apart laps of opened coils on said charge support means.

3. A rotary hearth annealing furnace including stationary walls defininga generally annular furnace chamber, a rotary hearth disposed at thelower part of said furnace chamber, seven substantially equallycircumferentially spaced radially extending dividing walls carried bysaid rotary hearth and movable t erewith, said dividing walls extendingin close fitting proximity to said furnace walls whereby said furnacechamber is divided into seven substantially identical, circumferentiallydisposed charge compartments, means for rotating said rotary hearth andcharge compartments in step-by-step movement and indexing saidcompartments successively at seven equally spaced charge treatingstations, a charge opening in the furnace wall at the first chargetreating station, means for loading a charge into the charge compartmentdisposed at ll said first station, a charge discharge opening in saidfurnace wall at charge station seven, counting from said first stationin the direction of rotation of said hearth, means for withdrawing acharge from the charge compartment disposed at said station seven,atmosphere conducting means adapted to connect the lower portion of thecharge compartment at the first station with the lower portion of thecharge compartment at station seven, atmosphere conducting means adaptedto connect the upper portion of the charge compartment at the firststation with the charge compartment at station seven, fan means forcreating a circulation of atmosphere through the charge compartmentsdisposed at said first station and station seven and the chargessupported therein, atmosphere conducting means between the lower portionof station two and the lower portion of station six, atmosphereconducting means between the upper portion of the station two and theupper portion of station six, means for creating a circulation ofatmosphere through the charge compartments at said stations two and sixand the charges therein, means outside of said furnace chamber forheating a portion of the furnace atmosphere, atmosphere conducting meansbetween the lower part of station three and said atmosphere heatingmeans and between said atmosphere heating means and the upper part ofstation three, means for creating and maintaining circulation ofatmosphere through said atmosphere heating means and through the chargecompartment disposed at station three whereby the charge therein isheated while at station three, a second atmosphere heating meansdisposed outside of said furnace chamber, atmosphere conducting meansbetween the lower portions of stations four and five and said secondatmosphere heating means and between said second atmosphere heatingmeans and the upper portions of stations four and five, and means forcirculating atmosphere between said second atmosphere heating means andthe charge compartments disposed at stations four and five whereby thecharges disposed therein may be supplied with heat.

4. A rotary hearth annealing furnace including stationary walls defininga generally annular furnace chamber, a rotary hearth disposed at thelower part of said furnace chamber, seven substantially equallycircumferentially spaced radially extending dividing walls carried bysaid rotary hearth and movable therewith, said dividing walls extendingin close fitting proximity to said furnace walls whereby said furnacechamber is divided into seven substantially identical, circumferentiallydisposed charge compartments, means for rotating said rotary hearth andcharge compartments in step-by-step movement and indexing saidcompartments successively at seven equally spaced charge treatingstations, a charge opening in the furnace wall at the first chargetreating station, means for loading a charge into the charge compartmentdisposed at said first station, a charge discharge opening in saidfurnace wall at charge station seven, counting from said first stationin the direction of rotation of saidrhearth, means for withdrawing acharge from the charge compartment disposed at said station seven,atmosphere conducting means adapted to connect the lower portion of thecharge compartment at the first station with the lower portion of thecharge compartment at station seven, atmosphere conducting means adaptedto connect the upper portion of the charge compartment at the firststation with the charge compartment at station seven, fan means forcreating a circulation of atmosphere through the charge compartmentsdisposed at said first station and station seven and the chargessupported therein, atmosphere conducting means between the lower portionof station two and the lower portion of station six, atmosphereconducting means between the upper portion of the station two and theupper portion of station six, means for creating a circulation ofatmosphere through the charge compartments at said stations two and sixand'the charges therein, said last named atmosphere circulating meanscausing the atmosphere circulation in station two to be in a directionopposite to that in the first station and the circulation in station sixto be opposite that in station seven, means ouside of said furnacechamber for heating a portion of the furnace atmosphere, atmosphereconducting means between the lower part of station three and saidatmosphere heating means and between said atmosphere heating means andthe upper part of station three, means for creating and maintainingcirculation of atmosphere through said atmosphere heating means andthrough the charge compartment disposed at station three whereby thecharge therein is heated while at station three, a second atmosphereheating means disposed outside of said furnace chamber, atmosphereconducting means between the lower portions of stations four and fiveand said second atmosphere heating means and between said secondatmosphere heating means and the upper portions of stations four andfive, and means for circulating atmosphere between said secondatmosphere heating means and the charge compartments disposed atstations four and five whereby the charges disposed therein may besupplied with heat, the direction of flow of heated atmosphere from saidsecond atmosphere heating means through the charge compartments atstations four and five being opposite to the flow of heated atmospherethrough the charge compartment disposed at station three.

5. The method of annealing opened coils of strip metal which includesthe steps of moving a series of opened coils with their axes verticalthrough a series of treating stations in a furnace, removing annealedcoils at one of said stations and adding new coils at another station,heating said coils by forcing heated atmosphere vertically through theopened laps of the coils at a station spaced intermediate said stationswhere coils are removed and added, circulating atmosphere verticallythrough a pair of coils, one of which has been heated to annealingtemperature and is ready for cooling and the other of which has not yetbeen heated to annealing temperature, whereby said one coil is cooledand said other coil is preheated, alternating the direction of verticalflow of atmosphere through the laps of the coils at succeeding stationsof said series whereby the temperature of said coils is equalized, andmoving said coils in step-by-step manner whereby each coil of the seriesis successively preheated, heated to annealing temperature, and cooledby circulation of atmosphere vertically through the opened laps of thecoils.

' 6. A coil support unit for supporting an opened coil of strip metal ina rotary hearth furnace during annealing including a baffle plateportion having a circular opening therein, a perforate grid structureextending across said circular opening and adapted to support an openedcoil thereon, side walls depending from said baflle plate member anddefining opposite sides of said unit, and bottom support members spacedfrom the coil engaging surface of said grid structure and lyingsubstantially in the plane of the lower edges of said side walls, saidbottom support members being spaced to provide open channels extendinggenerally in the same direction as said side walls and adapted toreceive means for elevating and conveying said coil support unit and acoil thereon, the inner end of said baflle plate member being concavelycontoured substantially on the radius of the inner wall of the furnacewith which the unit is to be used and the outer end of said baffle platebeing convexly contoured substantially on the radius of the outer wallof said furnace.

7. In a rotary hearth furnace for annealing opened coils of strip metalhaving spaced apart laps, stationary walls defining a generally annularcontinuous furnace chamber, a rotary hearth carrying walls, dividingsaid furnace chamber into a plurality of movable charge compartments,means for moving said hearth and charge compartments between a series ofcharge treating stations, said furnace walls having charging anddischarging openings therein, bafile members in said charge compartmentsand having perforate coil supporting and engaging areas and Y 13imperforate baflie areas spaced above said rotary hearth, means forcirculating a body of atmosphere vertically through and horizontallybetween the charge compartments disposed at a spaced apart pair of saidstations, atmosphere heating means disposed outside of said furnacechamber, and means for circulating a separate body of atmosphere in acontinuous flow through said atmosphere heating means and verticallythrough a charge compartment disposed at a station intermediate saidpair of stations, said imperforate baffie areas of said baffie platemembers being disposed to direct substantially all of said circulatingatmosphere through said perforate coil engaging and supporting areaswhereby said circulating bodies of atmosphere will be forced through thespaced apart laps of opened coils supported on said perforate coilsupporting areas.

8. In a movable hearth furnace for annealing opened coils of strip metalhaving spaced apart laps, stationary walls defining a continuous furnacechamber, a movable hearth having walls extending into and dividing saidfurnace chamber into a series ofmovable charge compartments, means formoving said hearth and charge compartmentssin step-by-steptravel'between a series of charge treating stations in said furnacechamber, said furnace walls having charging and discharging openings atthe first and last of said stations respectively, door means for closingsaid openings, baffle plate members in said charge compartments andhaving perforate coil supporting and engaging areas and imperforatebaflle areas spaced above said movable hearth, atmosphere conductingmeans between said first station and another of said stations that isspaced from said first station by one or more intermediate stations, fanmeans for circulating atmosphere between said first and said other ofsaid stations, atmosphere conducting means between the station nextahead of said first station and the station next behind said otherstation, fan means for circulating atmosphere through and between saidlast two named stations in a direction opposite to the direction ofcirculating between said first and said other stations, atmosphereheating means outside of said furnace chamber, and means for circulatinga separate body of atmosphere in a continuous flow through saidatmosphere heating means and vertically through a charge compartmentdisposed at one of said intermediate stations, said imperforate bafiieareas of said bafile plate members being disposed to directsubstantially all of said circulating atmosphere through said perforatecoil engaging and supporting areas whereby said circulating bodies ofatmosphere will be forced through the spaced apart laps of opened coilssupported on said coil supporting areas.

9. In a rotary hearth furnace for annealing opened coils of strip metal,stationary walls defining a generally annular continuous furnacechamber, a rotary hearth at the bottom of said furnace chamber, radiallyextending dividing walls carried by said rotary hearth and separatingsaid furnace chamber into a plurality of circumferentially arrangedsimilar charge compartments, means for rotating said rotary hearth anddividing walls in intermittent step-by-step movement whereby saidcompartments each progressively move to a series of work stations, acharging door in said furnace wall at a first or charging station, adischarging door in said furnace wall at the last or dischargingstation, said last station being circumferentially spaced from saidfirst station in the direction of rotation of said hearth by one or moreintermediate stations, opened coil support units having circularperforate coil engaging areas, means for supporting said coil supportunits for radial movement toward and away from said hearth and into andout of said charge compartments through said charging and dischargingdoors when said compartments are indexed respectively at said chargingand discharging stations, said coil support units when in said chargecompartments being disposed with their circular perforate coil engagingareas spaced 14 i above said rotary hearth whereby atmosphere may bemoved vertically through opened coils carried on said areas, said coilsupport units including baffle portions disposed to substantially blockthe vertical flow of atmosphere in said charge compartments exceptthrough said circular perforate coil engaging areas, means forconducting atmosphere between the lower part of one of said stations andthe lower part of another of said stations that is spaced from onestation by at least one intermediate station, means for conductingatmosphere between the upper part of said one station and the upper partof said other station, fan means for causing the atmosphere in said oneand said other of said stations to circulate there through and passvertically through opened coils in the charge compartments disposed atsaid stations, means for moving heated atmosphere vertically through acharge compartment and opened coil supported therein when indexed at aheating station between said one and said other of said stations wherebythe opened coil may be heated, and means disposed outside of saidstationary walls for supplying heat to the atmosphere being circulatedat said heating station.

10. A rotary hearth annealing furnace for annealing opened coils ofstrip metal having spaced apart laps including stationary Walls defininga generally annular continuous furnace chamber, a rotary hearth disposedat the lowerpart of said furnace chamber, a plurality of radiallyextending dividing walls carried by said rotary hearth and movabletherewith, said dividing walls extending in close proximity to saidfurnace walls whereby said furnace chamber is divided into a pluralityof charge compartments, means for supporting an opened coil of stripmetal in each of said charge compartments above said hearth and with itsaxis vertical, means for rotating said -rotary hearth and chargecompartments in step-by-step movement and indexing said compartments ata series of charge treating stations in said furnace chamber, means forloading a charge into the charge compartment disposed at one of saidstations, means for withdrawing a charge from the charge compartmentdisposed at another of said charge treating stations, means formaintaining an artificial gaseous atmosphere within said furnacechamber, means for circulating between a pair of charge compartmentsindexed at a particular pair of said work treating stations theatmosphere contained therein whereby heat exchange is effected betweenthe charges in said pair of charge compartments, gas heating meansdisposed outside of said furnace chamber, means for repeatedlycirculating a body of said artificial gaseous atmosphere verticallythrough another of said charge compartments disposed at another of saidcharge treating stations and said gas heating means whereby the chargein said last named charge compartment is heated, each of said means forsupporting an opened coil of strip metal including a bafiie platedisposed to direct substantially all of the atmosphere being circulatedthrough the charge compartments vertically through the spaced apart lapsof opened coils disposed on said supporting means, a second gas heatingmeans disposed outside of said furnace chamber, and means forcirculating a second body of artificial gaseous atmosphere through saidsecond heating means and vertically through another of said chargecompartments indexed at still another of said charge treating stations.

11. A rotary hearth furnace as defined in claim 10 in which said meansfor loading a charge into the furnace includes a charge loading openingin said furnace wall at said one of said charge treating stations, doormeans for closing said loading opening, a purge chamber connected tosaid furnace chamber at said charge loading opening, said purge chamberhaving an outer door adapted to be opened to permit the entry of acharge into said chamber and to be closed thereafter, and means fordirecting an artificial gas atmosphere into said purge chamber and thecharge therein and permitting air to be urged therefrom.

12. A rotary hearth furnace as defined in claim 10 having a chargedischarge opening in said furnace wall at said another of said chargetreating station's, door means for closing said discharge opening, afinal cooling chamber connected to said furnace at said dischargeopening and adapted to receive a charge withdrawn from the furnace, saidcooling chamber having an outer door adapted to be opened to permitremoval of the charge and closed during the cooling operation, and meansfor forcing a cooling atmosphere through the charge in said coolingchamber.

13. A rotary hearth furnace as defined in claim 11 having a chargedischarge opening in said furnace wall at said another of said chargetreating stations, door means for closing said discharge opening, afinal cooling chamber connected to said furnace at said dischargeopening and adapted to receive a charge withdrawn from the furnace, saidcooling chamber having an outer door adapted to be opened to permitremoval of the charge and closed during the cooling operation, and meansfor forcing a cooling atmosphere through the charge in said coolingchamber.

14. In a rotary hearth annealing furnace for annealing opened coils ofstrip metal, stationary walls defining a generally annular continuousfurnace chamber, a rotary hearth disposed at the lower part of saidfurnace chamber and forming the bottom wall thereof, a plurality ofradially extending dividing walls carried by said rotary hearth andmovable therewith, said dividing walls extending in close proximity tosaid furnace walls whereby said furnace chamber is divided into aplurality of charge compartments, means for rotating said rotary hearthand charge compartments in step-by-step movement and indexing saidcompartments at a series of charge treating stations, a charge loadingopening in said furnace wall at one of said charge treating stations, acharge loading carriage supported for movement into and out of thecharge compartment indexed at said charge loading opening, a

coil support unit adapted to be carried by said charge loading carriageand to support an opened coil thereon, said charge loading carriageincluding means for lifting said coil support unit and the coil thereonabove the level of said rotary hearth and lowering said unit and coilinto position on said rotary hearth after said carriage is moved intosaid charge compartment whereby said charge loading carriage may befreely withdrawn from the charge compartment, said coil support unitincluding a bafiie portion, the bathe portion having a circular opening,and a perforate coil engaging area extending across said circularopening, said coil support unit fitting within the walls of the furnacecharge compartment, having an atmosphere opening aligned with anatmosphere opening in the furnace wall, and being adapted to channelsubstantially all of the atmosphere that passes into the chargecompartment through the opened coil supported on the perforate coilengaging area.

References Cited in the file of this patent UNITED STATES PATENTS1,546,532 Baily July 21, 1925 1,727,192 Baily Sept. 3, 1929 1,903,909Cope et al Apr. 18, 1933 1,938,306 Webb Dec. 5, 1933 2,143,905 AhlmannIan. 17, 1939 2,234,871 MacDonald Mar. 11, 1944 2,499,926 Lloyd -i Mar.7, 1950 2,507,274 Sevenich May 9, 1950 2,622,861 Talley Dec. 23, 19522,777,683 Ferguson Jan. 15, 1957 FOREIGN PATENTS 500,824 Germany June25, 1930 OTHER REFERENCES German patent application 13 31,215, printedFeb. 2, 1956.

5. THE METHOD OF ANNEALING OPENED COILS OF STRIP METAL WHICH INCLUDESTHE STEPS OF MOVING A SERIES OF OPENED COILS WITH THEIR AXES VERTICALTHROUGH A SERIES OF TREATING SATIONS IN A FURNACE, REMOVING ANNEALEDCOILS AT ONE OF SAID STATIONS AND ADDING NEW COILS AT ANOTHER STATION,HEATING SAID COILS BY FORCING HEATED ATMOSPHERE VERTICALLY THROUGH THEOPENED LAPS OF THE COILS AT A STATION SPACED INTERMEDIATE SAID STATIONSWHERE COILS ARE REMOVED AND ADDED, CIRCULATING ATMOSPHERE VERTICALLYTHROUGH A PAIR OF COILS, ONE OF WHICH HAS BEEN HEATED TO ANNEALINGTEMPERATURE AND IS READY FOR COOLING AND THE OTHER OF WHICH HAS NOT YETBEEN HEATED TO ANNEALING TEMPEATURE, WHEREBY SAID ONE COIL IS COOLED ANDSAID OTHER IS PREHEATED, ALTERNATING THE DIRECTION OF VERTICAL FLOW OFATMOSPHERE THROUGH THE LAPS OF THE COILS AT SUCCEDDING STATIONS OF SAIDSERIES WHEREBY THE TEMPERATURE OF SAID COILS IS EQUALIZED, AND MOVINGSAID COILS IN STEP-BY-STEP MANNER WHERE-